The disclosed invention is directed generally to holographic center high mounted stoplights for vehicles, and more particularly to a holographic center high mounted stoplight that includes a source of nearly collimated light and an expanding lens to produce an ultimately diverging reconstruction beam from the nearly collimated light.
Present federal regulations require center high mounted stoplights (CHMSLs) in addition to the standard stoplights mounted in the rear portion of an automobile. The high mounted stoplights are intended to maximize the visibility of the automobile braking indicators to drivers following the braking vehicle, and are commonly mounted on or near the rear window of an automobile.
High mounted stoplights have commonly been implemented as a standard lenticular lens, a red filter, an illuminating incandescent bulb, and a reflector enclosed in a housing that is typically secured adjacent the top or bottom of an automobile rear window. However, the bulky housing partially obscures the rearward vision of the driver, and moreover imposes limitations on the design of the automobile.
Center high mounted stoplights have been also integrated into automobile body parts such as rear decks, spoilers, roofs, which to some degree substantially reduce or remove the rearward vision problem. However, such stoplights are complex and may impose limitations on the design of the automobile.
Holographic center high mounted stoplights have also been developed in order to efficiently meet the stoplight regulations. Known holographic center high mounted stoplights include those which utilize a nearly collimated reconstruction beam for efficient utilization of the light output of an incandescent bulb, and for compactness of the stoplight hologram. However, a consideration with the use of a collimated reconstruction beam is the potential hazard of the zero order (non-diffracted) reconstruction illumination that is transmitted by the stoplight hologram. As is well known, holograms have rather restrictive requirements for both wavelength and angle of the reconstruction light. These requirements would not normally be met by all of the light emitted by a standard light source, and thus a significant amount of light is not diffracted by a hologram. The non-diffracted light could comprise near collimated light of high intensity that could have a temporary blinding effect on the driver of a vehicle that is following a vehicle whose holographic stoplight is activated.
A possible implementation utilizing a non-collimated reconstruction beam would involve the use of a reflector that produces a diverging beam. However, this would require an inordinately larger stoplight hologram, or a reflector would having unacceptably reduced collection efficiency as a result of the space constraints.